In general, in an image forming apparatus of an electrophotographic type, an electrostatic latent image formed on a photosensitive drum as an image bearing member is developed as a toner image with a developer containing a toner and a carrier by a developing device as a developing means. In such a developing device, in a circulating path in a developing container, the toner and the carrier are triboelectrically charged by feeding the developer while stirring the developer by rotating a feeding screw. The developer containing the toner and the carrier gradually lowers in charging performance of the carrier by continuous circulation of the carrier which is not consumed by image formation while being subjected to friction in the developing container. For this reason, ensuring of an average charge performance of the carrier in the developer has been conventionally made by discharging a part of the developer by overflow through a discharge opening provided in the developing container while supplying a new (fresh) developer to the developing container (Japanese Patent Publication Hei 2-21591).
Further, a developing device constituted so that a force, with respect to a circumferential direction or an outward radial direction, acting on the developer by rotation of the feeding screw in an opposing region to a developer discharge opening is made smaller than a force in another region has been proposed (Japanese Laid-Open Patent Application (JP-A) 2000-112238). Specifically, a constitution in which a blade of the feeding screw in the opposing region to the developer discharge opening is made small or a constitution in which the blade is omitted (removed) is employed.